Book/Dissertation / PhD Thesis

FZJ-2019-05253

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Current-induced magnetization switching in a model epitaxial Fe/Au bilayer

Gospodaric, P. -. G. (Corresponding author)FZJ*

2019
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-423-2

Please use a persistent id in citations: http://hdl.handle.net/2128/23299

Abstract: In electronics, the application of novel spintronic three-terminal memory devices is proposed to facilitate further improvements of the performance of electronic components. A promising write-mechanism in a spintronic memory is based on the purely electricalswitching of the magnetization by $\textit{spin-orbit torque}$ (SOT) that can occur, for example, at the interface of heavy metal (HM)/ferromagnetic metal (FM) bilayers. This thesis presents a study of the epitaxial model HM/FM system Au(4 nm)/Fe(1- 1.5 nm)/MgO(001) using magneto-transport measurements and Kerr microscopy. The Au/Fe bilayers were photolithographically patterned into Hall bars in order to study their magnetic and magneto-transport properties. The Au/Fe bilayer Hall bars on MgO(001) substrate exhibit a strong in-plane easy magnetization axis and a cubic magnetic anisotropy in the film plane dominated by the magneto-crystalline term of the Fe(001) layer. In the chosen geometry of the samples the easy magnetization directions coincide with the extrema of the transversal voltage induced by the planar Hall effect (PHE). Therefore, a switching of the magnetization from one easy direction to another can be detected by measuring the PHE-voltage. Furthermore, Kerr microscopy revealed the formation of stripe-shaped magnetic domains separated by 90$^\circ$ domain walls aligned perpendicular to the Hall bar. A combined measurement of PHE-voltage and acquisition of Kerr images has shown that the measured PHE-voltage is most considerably affected by the domain configuration within the central area of the Hall cross. Based on this findings, the influence of electrical currents on the magnetization in the Fe(001) layer was investigated via measurements of the PHE combined with Kerr microscopy. At room temperature, a current density beyond 10$^{7}$ A/cm$^{2}$ induces an Oersted field, which in the Fe(001) layer points in-plane in the direction perpendicular to the long axis of the Hall bar and can exceed the coercive field B$_{c}$=0.65$\pm$0.05 mT for the 90$^\circ$ switch of the magnetization. Moreover, a current density beyond 1.4$\cdot$10$^{7}$ A/cm$^{2}$ with an alternating polarity can be employed for reproducible electrical switching of the magnetization in the Au/Fe/MgO(001) Hall bars between multiple stable states. Kerr microscopy confirmed that a variation of the applied current density changes the domain structure at the Hall bar cross. The change of the domain structure scales with the applied current density and can be read-out as a change in the PHE-voltage. The PHE measurements at T<50 K indicate a presence of an additional current-induced field up to 2.5 mT in the direction normal to the film surface.

Note: Universität Duisburg, 2019

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Contributing Institute(s):

1. Elektronische Eigenschaften (PGI-6)

Research Program(s):

1. 522 - Controlling Spin-Based Phenomena (POF3-522) (POF3-522)

Appears in the scientific report 2019

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